Title of the Research Project:
Turning Trash into Treasure
Dr Edmund Chun Ming Tse
Summary of the Research:
The research project is to develop an electrocatalytic method to upcycle chloride ion (Cl-) derived from polyvinyl chloride1 (PVC), a commonly used plastic product, into hypochlorite ion (OCl-), which is an active ingredient of bleach.
Synthetic polymers, including PVC, have contributed 11% to the total mass of municipal waste2,3. Also, PVC can be recycled for at most 7 times4. After that, it may end up at the landfill site. To utilize the PVC waste as much as possible, hydrogen chloride (HCl) would be extracted from the PVC waste, followed by converting HCl into NaOCl.
However, the traditional process of turning Cl- into OCl- in the chloro-alkali industry releases toxic and corrosive chlorine gas (Cl2). Therefore, the scholar would develop an electrocatalytic system to oxidize Cl- into OCl- in a single step.
1. O'Mara MM. High-temperature pyrolysis of poly(vinyl chloride): Gas chromatographic-mass spectrometric analysis of the pyrolysis products from PVC resin and Plastisols. Journal of Polymer Science Part A-1: Polymer Chemistry. 1970;8(7):1887–1899. doi:10.1002/pol.1970.150080724
2. Gibb BC. Nature Chem. 2019;11:394. Schneiderman, D. K.
3. Hillmyer MA. Macromolecules, 2017;50:3733.
4. Australian Government. National waste policy: Case study. 2021
Summary of the Work to be Undertaken by the Scholar:
-First, commercially available aqueous NaOCl solution would be added to a membrane cell with platinum as the anode, graphite as the cathode, and Nafion as the ion-exchange membrane. Then, a corrosion test would be performed. The purpose of this step is to investigate whether these materials can withstand the corrosion by NaOCl solution, which is our intended product.
- If there is no serious corrosion occurred in the first step, concentrated NaCl solution would be added to the above membrane cell.
- After that, compressed air (which contains around 21% of oxygen) would be bubbled into the concentrated sodium chloride solution. NaOCl, hydrogen, and sodium hydroxide are produced. The scholar hypothesized that platinum at the anode would be the catalyst for the formation of OCl-.
- Since NaCl+1/2 O2 → NaOCl is an endergonic reaction, a driving force in the form of electrical potential is required.
-The amount of NaOCl would be determined by first adding it to a known concentration of sulphuric acid and excess potassium iodide solution. Then, titrate the solution mixture with a known concentration of sodium thiosulphate. During the titration, a starch solution is added as the indicator. The endpoint is reached when the solution turns from blue-black to colourless. The number of moles of NaOCl can be deduced by observing the amount of sodium thiosulphate consumed.
- The reaction conditions would be recorded, and the yield of NaOCl would be calculated at the end. The magnitude of the electrical potential applied during electrolysis and the concentration of the added brine will be varied for comparison. Through comparison, the optimized reaction condition that maximizes the yield of NaOCl can be determined.